Compositions of Matter, and Methods of Removing Silicon Dioxide

ABSTRACT

Some embodiments include methods of removing silicon dioxide in which the silicon dioxide is exposed to a mixture that includes activated hydrogen and at least one primary, secondary, tertiary or quaternary ammonium halide. The mixture may also include one or more of thallium, BX 3  and PQ 3 , where X and Q are halides. Some embodiments include methods of selectively etching undoped silicon dioxide relative to doped silicon dioxide, in which thallium is incorporated into the doped silicon dioxide prior to the etching. Some embodiments include compositions of matter containing silicon dioxide doped with thallium to a concentration of from about 1 weight % to about 10 weight %.

TECHNICAL FIELD

Compositions of matter, and methods of removing silicon dioxide.

BACKGROUND

Silicon dioxide is frequently utilized during integrated circuitfabrication. The silicon dioxide may be utilized for its insulativeproperties. Additionally, or alternatively, the silicon dioxide may beutilized for its etch properties in that it can be a sacrificialmaterial that may be removed selectively relative to other materials, ormay be a protective material which is selectively retained while othermaterials are removed.

In some applications it is desired to remove only a portion of a silicondioxide layer, while leaving the remainder of the silicon dioxide layer.For instance, it may be desired to strip the upper surface of a silicondioxide layer to remove contaminants or possible non-homogeneities priorto utilizing the silicon dioxide layer as a gate dielectric.

As another example, it may be desired to form silicon dioxide within atrench to fabricate a trenched isolation region. The silicon dioxide maybe initially formed to fill, or even overfill the trench; and it may bedesired to remove some of silicon dioxide so that the silicon dioxideultimately is recessed to beneath an uppermost level of the trench.

A method for removing a portion of a silicon dioxide layer is to utilizea diffusion-limited etch. Such etch will stop after some of the silicondioxide layer is removed, and before an entirety of the silicon dioxidelayer is removed. An example diffusion-limited etch is described withreference to FIGS. 1-3.

FIG. 1 shows a portion of a semiconductor construction 10. Theconstruction includes a semiconductor substrate (or base) 12, and alayer 14 over the substrate.

Substrate 12 may comprise, consist essentially of, or consist of, forexample, monocrystalline silicon lightly-doped with background p-typedopant. The terms “semiconductive substrate,” “semiconductorconstruction” and “semiconductor substrate” mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove. Although semiconductor substrate 12 is shown to be homogeneous,in some applications the substrate may comprise one or more electricallyinsulative materials, electrically conductive materials, and/orsemiconductive materials associated with integrated circuit fabrication.

Layer 14 may comprise, consist essentially of, or consist of silicondioxide.

Layer 14 is exposed to an etchant comprising NH_(x)F_(y) and H^(*),where “x” and “y” are integers greater than or equal to 1, and H^(*) isan activated form of hydrogen. The activated form of hydrogen may resultfrom, for example, flowing a hydrogen-containing species (for instance,NH₃) through a plasma.

The etchant removes silicon dioxide from layer 14, but in the process ofsuch removal, an ammonium fluorosilicate by-product is formed. Theammonium fluorosilicate by-product eventually creates a cap across layer14. The ammonium fluorosilicate cap is impermeable to the etchant, andaccordingly impedes further diffusion of the etchant to layer 14. Suchprevents further etching of layer 14. The self-limiting nature of theetch restricts the amount of silicon dioxide removed by the etchantAccordingly, the etchant removes only a thin portion from across exposedsurfaces of the silicon dioxide. In some applications, the etchant maystrip less than or equal to about 5 nanometers from exposed surfaces ofthe silicon dioxide.

FIG. 2 shows construction 10 after removal of some of layer 14, andafter formation of the ammonium fluorosilicate (NH₄)₂SiF₆ cap 16 overthe remaining portion of layer 14.

In subsequent processing, the ammonium fluorosilicate cap may beremoved. Such removal may be accomplished by, for example, heatingconstruction 10 to a temperature above 100° C. to volatilize theammonium fluorosilicate and/or by utilizing an etch selective forammonium fluorosilicate relative to the underlying silicon dioxide. FIG.3 shows construction 10 at a processing stage after removal of theammonium fluorosilicate cap 16 (FIG. 2).

The technology of FIGS. 1-3 is useful for cleaning and recessing silicondioxide. However, there are some applications where the technology leadsto less than satisfactory results. For instance, the technology is notparticularly selective for undoped silicon dioxide relative to dopedsilicon dioxide (with doped silicon dioxide being, for example,fluorosilicate glass, borophosphosilicate glass, and phosphosilicateglass), and there are applications in which such selectivity would bedesired. As another example, the etching technology may be tooaggressive during applications in which it is desired to recess silicondioxide within a trench or other opening. The silicon dioxide withinsuch openings may have keyholes or seams extending therein, and the etchmay expand such keyholes and seams to produce undesired results.

It would be desirable to develop improved etch technologies for removingsilicon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are diagrammatic, cross-sectional views of a portion of asemiconductor construction shown at various stages of a prior art etchsequence.

FIGS. 4-6 are diagrammatic, cross-sectional views of a portion of asemiconductor construction shown at various process stages of anembodiment.

FIGS. 7-9 are diagrammatic, cross-sectional views of a portion of asemiconductor construction shown at various process stages of anembodiment.

FIGS. 10-12 are diagrammatic, cross-sectional views of a portion of asemiconductor construction shown at various process stages of anembodiment.

FIGS. 13-15 are diagrammatic, cross-sectional views of a portion of asemiconductor construction shown at various process stages of anembodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention includes embodiments in which new chemistries are utilizedfor diffusion-limited etching of silicon dioxide. Some embodimentsinclude incorporation of relatively large components in the etchant sothat geometric constraints limit penetration of the etchant into seams,keyholes, and other tight features. Other embodiments which may beadditional, or alternative, to the embodiments utilizing largecomponents include incorporation of components into one or both of theetchant and silicon dioxide-containing material to enhance selectivitybetween doped and undoped silicon dioxide.

An example embodiment process for incorporating large components into anetchant is described with reference to FIGS. 4-6.

FIG. 4 shows a portion of a semiconductor construction 20. Theconstruction includes a semiconductor substrate (or base) 22 having anopening 24 extending therein. The semiconductor substrate 22 maycomprise the same compositions discussed above for the substrate 12 ofFIG. 1.

The opening 24 may be a trench, and may ultimately be utilized forforming a trenched isolation region.

Electrically insulative material 26 is formed within opening 24. Theelectrically insulative material is shown to be a single homogeneouscomposition, but in some embodiments multiple different compositions maybe formed within the opening. Regardless, the insulative materialincludes silicon dioxide, and an exposed surface 27 of the insulativematerial comprises, consists essentially of, or consists of silicondioxide. The shown surface 27 extends into a keyhole (or seam) 28. Forpurposes of the discussion that follows, the entirety of insulativematerial 26 may be considered to be silicon dioxide in the shownembodiment.

It is desired to recess material 26 within opening 24 utilizingdiffusion-limited etching so that only a limited amount of the material26 is removed. A problem with prior art methods (such as the methodsdiscussed above with reference to FIGS. 1-3) is that the etchantsutilized for diffusion-limited removal of silicon dioxide may penetrateinto the keyhole and expand the keyhole during the recessing ofinsulative material 26. The embodiment of FIG. 4 utilizesNH_(a)R_(b)F_(c) in place of the NH_(x)F_(y) of the prior art etchant ofFIG. 1. The labels “a”, “b” and “c” represent integers, with “a” beinggreater than or equal to 0; and “b” and “c” being greater than or equalto 1. The material NH_(a)R_(b)F_(c) thus represents a primary,secondary, tertiary or quaternary ammonium halide (the halide ofNH_(a)R_(b)F_(c) is shown to be fluorine, but in other embodiments otherhalides may be utilized in addition to, or alternatively to, fluorine).In some embodiments, the etchant may comprise multiple differentcompositions represented as NH_(a)R_(b)F_(c), and thus may comprise oneor more of a primary, secondary, tertiary and quaternary ammoniumhalide. In some embodiments, the NH_(a)R_(b)F_(c) may include acomposition selected from the group consisting of propargylammoniumhalide, tetraalkylammonium halide, and mixtures thereof.

The embodiment of FIG. 4, like that of FIG. 1, utilizes the activatedform of hydrogen (H^(*)); and such activated form of hydrogen may resultfrom, for example, flowing a hydrogen-containing species (for instance,NH₃) through a plasma.

As indicated above, in some embodiments the NH_(a)R_(b)F_(c) may have“a” equal to 0, and thus may be NR_(b)F_(c). In such embodiments, theetchant may utilize a mixture of NR_(b)F_(c) and NH₃, with the NH₃ beingthe source of hydrogen.

The etchant may be in any suitable phase, and in some embodiments maycorrespond to a gaseous mixture.

The relative amounts of NH_(a)R_(b)F_(c) and activated hydrogen in themixture may be the same as the relative amounts of ammonium fluoride andactivated hydrogen in the prior art mixtures, and the etching conductedutilizing NH_(a)R_(b)F_(c) may occur under the same pressure,temperature and other conditions as are used in the prior art methodswith ammonium fluoride and activated hydrogen.

FIG. 5 shows construction 20 after removal of some of the silicondioxide-containing material 26, and after formation of adiffusion-limiting fluorosilicate layer 29 across silicondioxide-containing material 26. The removal of some of the silicondioxide-containing material 26 has decreased a height of the material 26within opening 24 from a first elevational level shown in FIG. 4 to thesecond elevational level shown in FIG. 5.

The diffusion-limiting fluorosilicate layer only extends across an uppersurface of silicon dioxide-containing material 26, and not into keyhole28 due to the large size of the NH_(a)R_(b)F_(c) precluding suchcomposition from entering the keyhole and creating the fluorosilicate.Thus, etching has not occurred within the keyhole and the prior artproblem of blowing out, or extending, a keyhole or seam has beenavoided. In order to avoid penetration of the etchant into a keyhole orseam, it can be desired that the only ammonium halides in the etchantare ammonium halides having a substantial amount of steric hindrance,and accordingly to avoid having ammonium fluoride itself (NH₄F) in themixture. Ammonium fluorides that may have desired steric hindrance arequaternary ammonium halides (NR₄X, where “R” is an organic group and “X”is a halide). In some embodiments, the quaternary ammonium halides mayhave two or more “R” groups which are different from one another, and inother embodiments all of the “R” groups in a quaternary ammonium halidemay be the same as one another. The “R” groups of the quaternaryammonium fluorides may each contain at least five carbon atoms in someembodiments.

The layer 29 will be some derivative of ammonium fluorosilicate (forinstance, may comprise a quaternary ammonium fluorosilicate), and may beremoved utilizing heat and/or etching as discussed above for removal ofthe fluorosilicate layer 16 of prior art FIG. 2. FIG. 6 showsconstruction 20 after removal of fluorosilicate layer 29 (FIG. 5).

Another example embodiment process in which it may be useful toincorporate large components into a silicon dioxide etchant is describedwith reference to FIGS. 7-9.

FIG. 7 shows a portion of a semiconductor construction 30. Theconstruction includes a semiconductor substrate (or base) 32, a silicondioxide-containing layer 34 extending across the substrate, and apatterned silicon nitride-containing material 36 over the silicondioxide-containing layer.

The semiconductor substrate 32 may comprise the same compositionsdiscussed above for the substrate 12 of FIG. 1.

The silicon dioxide-containing layer 34 may comprise, consistessentially of, or consist of silicon dioxide.

The silicon nitride-containing material 36 may comprise, consistessentially of, or consist of silicon nitride. Material 36 may bepatterned utilizing, for example, photolithographic processing.Specifically, a photolithographically-patterned photoresist mask (notshown) may be formed over an expanse of material 36, a pattern may betransferred from the photoresist mask to material 36 with one or moresuitable etches, and the photoresist mask may then be removed to leavethe construction of FIG. 7. The patterned silicon nitride-containingmaterial 36 defines a gap 38 extending therethrough to silicondioxide-containing layer 34.

The construction of FIG. 7 may be utilized to pattern transistor activeregions, and accordingly a portion of silicon dioxide-containing layer34 within the gap 38 may ultimately may be incorporated into atransistor gate dielectric. Prior to such incorporation, an uppersurface of the exposed segment of layer 34 is stripped to removecontaminants that may be associated with such upper surface. Thestripping may be accomplished utilizing a diffusion-limited etch of thetype described above with reference to FIGS. 4-6. Accordingly,construction 30 is shown exposed to NH_(a)R_(b)F_(c) and activatedhydrogen.

FIG. 8 shows construction 30 after removal of some of the silicondioxide-containing layer 34, and after formation of a fluorosilicatelayer 40 over a remaining portion of the silicon dioxide-containinglayer. The fluorosilicate layer limits diffusion of etchant to theremaining portion of silicon dioxide-containing layer 34 within gap 38,and thus stops the etching of layer 34.

A problem with prior art methods for removal of silicon dioxide inapplications like those of FIGS. 7 and 8 is that such methods may allowetchant to penetrate under material 36. Such penetration may causesilicon dioxide-containing layer 34 to become recessed under thematerial 36. In contrast, the etching conditions of the embodimentsdescribed herein may utilize etch materials having too much sterichindrance to penetrate under material 36, and accordingly may avoid theprior art problem.

The fluorosilicate layer 40 may be subsequently removed utilizing one orboth of thermal treatment an etching, and FIG. 9 shows construction 30after removal of such fluorosilicate layer.

As discussed above, one of the problems with prior art methods fordiffusion-limited removal of silicon dioxide is that such methods mayhave poor selectivity between undoped silicon dioxide and doped silicondioxide. For purposes of interpreting this disclosure, undoped silicondioxide means silicon dioxide and having less than 0.01 weight-percent(weight %) dopant; and doped silicon dioxide means silicon dioxide andhaving greater than or equal to 0.1 weight % dopant. FIGS. 10-12illustrate an embodiment for improving selectivity of removal of undopedsilicon dioxide relative to doped silicon dioxide.

Referring to FIG. 10, a portion of a semiconductor construction 50 isillustrated. The construction includes a semiconductor substrate (orbase) 52, and a pair of silicon dioxide-containing materials 54 and 56over the substrate 52.

The semiconductor substrate 52 may comprise the same compositionsdiscussed above for the substrate 12 of FIG. 1.

The silicon dioxide-containing material 54 may be undoped silicondioxide, and the silicon dioxide-containing material 56 may dopedsilicon dioxide. The doped silicon dioxide may correspond to, forexample, borophosphosilicate glass, phosphosilicate glass,fluorosilicate glass, etc.. Accordingly, the doped silicon dioxide maycontain at least 0.1 weight %, each, of one or more of phosphorus, boronand fluorine. Although materials 54 and 56 are shown one next toanother, other combinations of such materials are contemplated.

FIG. 10 shows materials 54 and 56 exposed to an etchant mixturecontaining NH_(x)F_(y), H^(*), and “D”, where “x” and “y” are integersgreater than or equal to 1, H^(*) is an activated form of hydrogen, and“D” is an additive to enhance selectivity. The etchant mixture may be inany suitable phase, and may, for example, be in a gaseous phase.

The additive “D” may comprise thallium, and may be present in the formTlX_(n), where “X” is a halide and “n” is an integer greater than orequal to 2. For instance, the thallium may be present as thalliumchloride. If the additive “D” comprises thallium, the thallium may bepresent in the etchant mixture to a concentration of from about 1 weight% to about 10 weight %. In addition to thallium, or alternatively tothallium, the additive “D” may comprise one or both of aphosphorus-containing composition and a boron-containing composition.For instance, the additive may comprise one or both of PX₃ and BQ₃;where “X” and “Q” are halides that may be the same as one another ordifferent from one another. If the additive comprises phosphorus, suchmay be present to a concentration of from about 0.1 weight % to about 3weight %; and if the additive comprises boron such may be present to aconcentration of from about 0.1 weight % to about 3 weight %. Inaddition to, or alternatively to, one or more of thallium, phosphorusand boron, the additive “D” may comprise one or more carbon-containingcompositions (i.e., organic compositions) such as one or more alkenes(for instance propylene and/or ethylene). The carbon may be present to aconcentration of from about 0.1 weight % to about 3 weight %.

The addition of the additive changes a rate at which a diffusion barrier(i.e., the fluorosilicate) is formed over the doped silicon dioxiderelative to the undoped silicon dioxide. There is often a minorvariation in the rate at which the fluorosilicate is formed over dopedsilicon dioxide relative to undoped silicon dioxide even utilizing priorart methods, in that the doped silicon dioxide will etch a little slowerthan the undoped silicon dioxide. The introduction of one or more of theabove-discussed additives “D” to the etchant mixture enhances the etchrate difference between the undoped silicon dioxide and the dopedsilicon dioxide so that much less of the doped silicon dioxide isremoved relative to the undoped silicon dioxide.

Although the etchant mixture of FIG. 10 is shown to contain ammoniumfluoride (NH_(X)F_(y)), in other embodiments the etchant mixture maycomprise a different ammonium halide in addition to, or alternativelyto, ammonium fluoride. Also, in some embodiments the methodology of FIG.4-6, or 7-9, may be combined with that of FIGS. 10-12, and accordinglythe ammonium fluoride of FIG. 10 may be replaced with theNH_(a)R_(b)F_(c) discussed above (or with a material having the generalformula NH_(a)R_(b)X_(c), where “X” is a halide).

FIG. 11 shows construction 50 at a processing stage subsequent to thatof FIG. 10, and shows undoped silicon dioxide 54 selectively etchedrelative to doped silicon dioxide 56. FIG. 11 also shows fluorosilicatematerials 58 and 60 formed over the undoped silicon dioxide 54 and thedoped silicon dioxide 56, respectively. The fluorosilicate materials 58and 60 may have the same composition as one another, or may vary incomposition from one another due to fluorosilicate 60 being formed overdoped silicon dioxide while fluorosilicate 58 is formed over undopedsilicon dioxide.

The fluorosilicates 58 and 60 may be removed by one or both of a thermaltreatment and etching to form the structure shown in FIG. 12.

The embodiment of FIGS. 10-12 enhances selectivity for undoped silicondioxide relative to doped silicon dioxide by providing various additiveswithin an etchant. Another method for enhancing the selectivity isprovide additive to the doped silicon dioxide, as discussed withreference to FIGS. 13-15.

FIG. 13 shows a portion of a semiconductor construction 70. Theconstruction includes a semiconductor substrate (or base) 72, and a pairof silicon dioxide-containing materials 74 and 76 over the substrate 72.Although materials 74 and 76 are shown one next to another, othercombinations of such materials are contemplated.

The semiconductor substrate 72 may comprise the same compositionsdiscussed above for the substrate 12 of FIG. 1.

The silicon dioxide-containing material 74 is undoped silicon dioxide,and the silicon dioxide-containing material 76 is doped silicon dioxide.The doped silicon dioxide may correspond to, for example,borophosphosilicate glass, phosphosilicate glass, fluorosilicate glass,etc. Accordingly, the doped silicon dioxide may contain at least 0.1weight %, each, of one or more of phosphorus, boron and fluorine. Insome embodiments, any of the phosphorus, boron and fluorine present inthe doped silicon dioxide is present to a concentration of less than orequal to about 5 weight %.

In addition to the phosphorus, boron and/or fluorine, the doped silicondioxide also contains an additive indicated by stippling 77 (only someof which is labeled). Such additive corresponds to thallium, and thethallium may be present to from about 1 weight % to about 10 weight %.The thallium may be provided as a thallium halide, such as, for example,thallium chloride.

Materials 74 and 76 are exposed to an etchant mixture containingNH_(x)F_(y) and H^(*), where “x” and “y” are integers greater than orequal to 1, and H^(*) is an activated form of hydrogen. The etchantmixture may be in any suitable phase, and may, for example, be in agaseous phase.

Although the etchant mixture of FIG. 13 is shown to contain ammoniumfluoride (NH_(x)F_(y)), in other embodiments the etchant mixture maycomprise a different ammonium halide in addition to, or alternativelyto, ammonium fluoride. Also, in some embodiments the methodology of FIG.4-6, or 7-9, may be combined with that of FIGS. 13-15, and accordinglythe ammonium fluoride of FIG. 13 may be replaced with theNH_(a)R_(b)F_(c) discussed above (or with a material having the generalformula NH_(a)R_(b)X_(c), where “X” is a halide).

FIG. 14 shows construction 70 at a processing stage subsequent to thatof FIG. 13, and shows undoped silicon dioxide 74 selectively etchedrelative to doped silicon dioxide 76. FIG. 14 also shows afluorosilicate materials 78 and 80 formed over the undoped silicondioxide 74 and the doped silicon dioxide 76, respectively. Thefluorosilicate materials 78 and 80 may have the same composition as oneanother, or may vary in composition from one another due tofluorosilicate 80 being formed over doped silicon dioxide whilefluorosilicate 78 is formed over undoped silicon dioxide.

The fluorosilicates 78 and 80 may be removed by one or both of a thermaltreatment and etching to form the structure shown in FIG. 15.

In some embodiments, the method of FIGS. 10-12 may be combined with thatof FIGS. 13-15 so that additive 77 (FIG. 13) is incorporated into thedoped silicon dioxide, and additive “D” (FIG. 10) is incorporated intothe etchant.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1-9. (canceled)
 10. The method of claim 11 wherein the mixture includesone or both of BX₃ and PQ₃, where X and Q are halides, and may be thesame as one another or different from one another.
 11. A method ofetching silicon dioxide comprising exposing the silicon dioxide to amixture that includes NH₃, a halide and one or more organiccompositions.
 12. The method of claim 11 wherein the one or more organiccompositions include at least one alkene.
 13. The method of claim 11wherein the one or more organic compositions include one or both ofpropylene and ethylene.
 14. The method of claim 11 wherein the mixtureincludes BF₃.
 15. The method of claim 11 wherein the mixture includesPF₃.
 16. The method of claim 11 wherein the silicon dioxide is undopedsilicon dioxide and is selectively etched relative to doped silicondioxide, the method further comprising incorporating thallium into thedoped silicon dioxide prior to the etching.
 17. The method of claim 16wherein the thallium is present in the doped silicon dioxide to aconcentration of from about 1 weight % to about 10 weight %.
 18. Themethod of claim 16 wherein the doped silicon dioxide comprises one ormore of phosphorus, boron and fluorine in addition to the thallium.19-20. (canceled)
 21. The method of claim 10 wherein the mixtureincludes activated hydrogen, PF₃ and thallium.
 22. The method of claim10 wherein the mixture includes activated hydrogen, BF₃ and thallium.23-24. (canceled)
 25. A composition of matter comprising silicon dioxidedoped with thallium to a concentration of from about 1 weight % to about10 weight %.
 26. The composition of matter of claim 25 furthercomprising one or more of phosphorus, boron and fluorine doped into thesilicon dioxide, with any of the phosphorus, boron and fluorine beingpresent to a concentration of less than about 5 weight %.
 27. The methodof claim 21 wherein the thallium is in the form of TlX_(n), wherein X isa halide and n is an integer greater than or equal to
 2. 28. The methodof claim 22 wherein the thallium is in the form of TlX_(n), wherein X isa halide and n is an integer greater than or equal to
 2. 29. The methodof claim 11 wherein the mixture includes TlX_(n), wherein X is a halideand n is an integer greater than or equal to 2; and wherein the mixturefurther includes activated hydrogen.